Dog’s Third Eyelid Is Swollen — Causes and Treatments

In this article we explain what is the Dog’s Third Eyelid, why does it get swollen, what’s the meaning of it, what are the main causes, and most common treatments.

In a nutshell…

  1. A common cause of swollen third eyelid is a condition called cherry eye when the tissue that holds the tear gland is too weak, so the gland falls out.
  2. Conjunctivitis and allergies can cause swelling and redness of the third eyelid.
  3. Horner’s syndrome, a neurological disorder, causes drooping eyelids, sunken eyes, and swollen third eyelid.
  4. When the dog suffers from dehydration or malnutrition, the third eyelid can become visible.
  5. Common treatments are eye drops, medication, antihistamines, and surgery.


Let’s go into more detail…


Dog’s Third Eyelid Is Swollen 

As a dog lover, you probably like to think you know everything there is to know about your beloved pet. But did you know that dogs have three eyelids?

If you didn’t, then that’s a good thing — it means that your dog never had any trouble with it.

However, it still might be a good idea to learn what to do when your dog’s third eyelid is swollen.

And I am more than happy to help!


What Is the Third Eyelid in a Dog?

Unlike the other two eyelids, which are made of skin and covered with fur, the third eyelid is a thin, wet membrane, usually called the nictitating membrane.

Normally, you can’t see it because it’s under the other two eyelids. But some dogs have a visible third eyelid of a greyish or clear color.

That includes the third eyelid, although it covers it only partially.

The nictitating membrane in dogs is, in fact, an evolutionary leftover and doesn’t serve as great of a purpose as in animals that have a full membrane.


What Does The Dog’s Third Eyelid Do?

Although it’s not as fully functional as it would be if it were full, the third eyelid serves numerous purposes.

For instance, it protects the inner corners of your dog’s eyes from damage and keeps dust and other contaminants away.

It also sweeps the eye and removes any dirt from its surface to the corners. From there, the dirt easily leaves the eye.

In addition, some dogs have tear ducts at the base of the third eyelid. When your dog blinks, the tears clean and lubricate the eye, adding a new level of protection on top.

Some glands in the tear ducts even contain certain types of antibodies.

That way, your dog’s third eyelid not only keeps his  eye moist but also protects it from eye infections!


Visible Third Eyelid — What It Means

As I’ve already mentioned, the third eyelid is typically invisible — in fact, you might not have even been aware it’s there!

It’s hidden behind the two regular eyelids, so you could only spot it if your dog is falling asleep or just waking up.

Pay attention to the inner corner of its eyes — that is where it usually shows up if you can see it at all.

Some dog breeds have a more protruding third eyelid, and if your dog does too, you don’t need to worry.

However, keep in mind that even a visible third eyelid is quite subtle — usually greyish, white, or clear.

If your dog’s third eyelid starts looking red or swollen, it’s a sign that something’s not right.

And if your dog has never had a visible third eyelid, but suddenly you start seeing it, it’s time to take your pup to a vet.

It’s always better to react quickly when your furry friend’s health is at stake.


Why Your Dog’s Third Eyelid Is Swollen

The eyelids, as well as the eyes, are quite sensitive, so you should take any redness, swelling, and other changes seriously.

The best course of action is to take your pet to a vet so that they can determine exactly what the issue is.

But in the meantime, here are a few conditions that could explain why your dog’s third eyelid is swollen…


Cherry Eye

Cherries might look appealing, but the eye condition that bears their name definitely doesn’t.

It’s characterized by a fleshy, red protrusion in the lower inner corner of the dog’s eye, so it’s quite easy to spot — and quite difficult to look away from.

This protrusion is actually the tear gland that is normally within the third eyelid.

When the tissue that holds it in place is weak or damaged, the tear gland prolapses right in the corner of the eye.

Your dog’s eye also might become more watery and prone to infections.

So far, no one really knows what causes cherry eye in dogs. Vets consider it to be a hereditary condition — one that is passed on from generation to generation.

Some dog breeds — usually small ones with short muzzles — are more prone to it than others.

So if you have Beagles, Boxers, terriers, Poodles, or Cocker Spaniels, be especially careful when it comes to their eye health.

While the disorder can affect any dog at any age, young ones are particularly vulnerable.

Cherry eye commonly appears in dogs under two years of age, and then becomes rarer as they grow older.

Every rule has an exception, though — even your older dog can get it, especially if it was prone to it in youth.



People can get conjunctivitis — but did you know that dogs can too?

Symptoms are similar as well: red and swollen eye, itchiness, excessive blinking, discharge.

The main difference is, of course, in the third eyelid — humans don’t have one, but dogs do, and it becomes inflamed like the rest of the eye.

Usually, viruses cause conjunctivitis, but so do foreign bodies such as smoke or dust, tumors, and other conditions.

The conjunctiva, a mucous membrane that covers the eyeball and lines the eyelids, becomes inflamed.

This membrane also lines the third eyelid, so it swells just as much as the other two.

In order to determine whether conjunctivitis is responsible for your dog’s swollen third eyelid, you need to consult a vet.

Even though this condition usually isn’t too serious, treatment is still necessary.


Neurological Disorders

Sometimes, the third eyelid prolapses because the nerve that supplies it doesn’t do its job properly anymore.

One such common nerve disorder is Horner’s syndrome, which affects the eye and facial muscles.

You can recognize it by drooping upper eyelids, constricted pupils, sunken eyes, and a red and swollen third eyelid.

There are many possible causes of Horner’s syndrome — middle or inner ear disease, bites, and injuries that damaged the nerve in the neck or chest, or tetanus.

But sometimes, the syndrome also occurs suddenly and without any noticeable cause.

It can resolve on its own just as spontaneously, though usually, some form of treatment is necessary.

All dogs can develop Horner’s syndrome, but certain breeds are more prone to it.

Among these and Golden Retrievers, Cocker Spaniels, and Collies.


Poor Physical Health

Your dog doesn’t necessarily have to suffer from a disorder or a disease to have a swollen and protruding third eyelid.

In fact, malnourishment and dehydration can also be culprits. Usually, these conditions cause the muscles around the eyes to relax and settle deeper into the socket.

Because of that, the third eyelid becomes much more obvious.

Malnourishment and dehydration can be just temporary issues that resolve on their own in a few weeks.

However, if the third eyelid remains swollen and visible even after that, it’s best to seek professional advice.


Scrolled Cartilage

T-shaped cartilage supports a dog’s third eyelid, and it can cause trouble in large dog breeds.

During the rapid growth phase, one part of this cartilage grows quicker and bends the whole structure, scrolling the eyelid too.

Basically, a scrolled eyelid resembles a pink or reddish mass in the corner of the eye that is quite similar to a cherry eye.

Actually, similarities can be so great that only careful examination under anesthesia shows that this is a different condition.

However, while the cherry eye often comes back even once it’s been resolved, scrolled cartilage doesn’t.

After the treatment, it’s highly unlikely that it will appear on the same eye — though there’s no guarantee for the other one.


Dog’s Third Eyelid – Treatment

Now you know what might be causing your dog’s third eyelid to swell. However, it’s just as important to know how to treat it.

Don’t forget to always take your dog to a vet in order to improve the chances of getting the best possible outcome.

After all, your furry best friend deserves that much.

Find below your best treatment options…



Conditions such as cherry eye and scrolled cartilage always require surgery.

Both of the procedures are quite common, usually successful, and leave no lasting consequences.

For the cherry eye, the surgeon will try to stitch the connective tissue together and put the prolapsed tear gland back in place.

If the damage is too great, they might have to create a new pocket to hold the tear gland.

As a last resort, the surgeon will remove the whole third eyelid along with the tear gland.

Most vets avoid going this far because removal of the tear gland comes with many issues — such as the chronic dry eye.

Cartilage surgery is even more straightforward – the surgeon identifies the overgrown part and completely removes it.

After both surgeries, your dog should take antibiotics and rest for at least a week.

The eyelid might still be visible for a while, but after a few days, it should go back to normal.


Eye Medicine or Antihistamines

For eye inflammations and infections that cause conjunctivitis, your vet will prescribe your dog some eye drops or antibiotics.

If they believe that allergies are the cause, then you’re likely to get antihistamines.

You might find it hard to get your dog to sit still while you put drops in its eyes, or even harder to make it take the prescribed medicine.

But your vet will surely explain how exactly to do it, so just follow their instructions.

You’ll see — it’s not as bad as it looks!


Treatment Depending on the Cause

Ultimately, the vet has to establish what the cause is for all of these conditions before they can start treating your dog.

Just prescribing pills or eye drops may be an easy solution, but it usually doesn’t make the problem go away in the long run.

A good vet will always perform the necessary tests and exams to establish exactly why your dog’s third eyelid is swollen and then proceed to treat the cause.


Final Thoughts

Noticing that your dog’s third eyelid is swollen is always a cause for alarm, but not for panic.

In most cases, the underlying conditions are easy to resolve and take only a few weeks of recovery.

After that, your dog will be just as happy and healthy as always!

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